Vacuum-meter



O, SEETZ VACUUM METER Filed Aug. 29, 1921 lruuslvtai O. 6e 1; t2

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I Patented June 23,1925.

UNITED STATES 1,542,913 PATENT OFFICE.

' osmn SEITZ, or IBADEN, swrrznarann, ASSIGNOR "r GLEICHRICHTER-AKTIEN-#GESELLSOHAIT, or GLARUS, swrrznan'ann.

VACUUM-METER.

Application filed nugust 29, 1921. Serial No. 486,261. (GRANTED UNDERTHE PROVISIONS OF THE AGE-OF MARCH 3, 1921, 41 STAT. L, 1313.)

To all whom it may crmcern; v

Be it known that I, OSKAR SEITz a citizen of the Swissv Republicresiding at Oberer Kappelerhof, Baden, gwitzerland, have in ventedcertain new and useful Improve ments in Vacuum Meters (for which I havefiled application in Switzerland, Nov. 8, 1919, Patent 'No. 87,996; inGermany, Nov. 14, 1919,

which the following is a specification. This invention has for itsobject toprovide an. improved compresslon' vacuummeter of the McLeodtype which is uni-- versally'employedfor measuring high vacua of theorder of less than a millimetre of mercury. fl

i This apparatus depends for its actionfon the compression toatmospheric pressure of a known volume of attenuated air containedoriginally in a measuring vessel including a .capillary extension. Thecompress1on is carried out by means of a barometric column and theresultant volume is read olf on the graduations of the'capillary tube. v

In such an apparatus, for the purpose of setting the elevated barometricmercury column relatively to the upper end of the capillary tube, (thatis to say up to the line y-y of Fig. I

ings) the vessel-containing the store of mercury must be-raised to agreater or less height according to the barometric height,

and the mercury meniscus inthe barometric tube must be visible.

For this reason those parts of the tubing in whichthe mercury meniscusmoves a e usually made of glass. However, in time a precipitate offinely subdivided mercurous 40 oxide and metallic mercury is depositedon the wall of-the barometric tube at the level of the y-y line, so thatthe level of the mercury meniscus is no longer visible.

. This is due to the fact that the mercury in the barometric tube isalways under the vacuum of the receiver,'and-the deposition of theprecipitate is promoted in a high vacuum. This does not occur so much inthe capillary tube because .in this tube'themercury is under higherabsolute pressure than in the barometric tube so that, asfound bexperience, no disturbing deposit of precipitate has been found to takeplace in the capillary tube,

Patent IIo. 355,l30; in France, Nov. '10 6,1920; and in Belgium, July 4,1921), of

1 in the accompanying draw-' fresh and careful setting of the mercurymeniscus. This necessitates the construction of the barometric tube oflass which, owing to its brittleness, is very lia le to breakdowns.

Further, for the purpose of cleaning, this I tube from the aforesaiddeposits it is necessary to have a special construction which is notfavourable to reliability in the opera-' tion of the apparatus.

All these drawbacks are obviated by the improve form-of vacuum-meteraccording to the present invention. The chief characteristic feature ofthis improved form consistsin this that the barometric tube is providedat its upper end o'nfa'level with the top of the capillary tube, with anenlargement having a very large cross section in proportion to.the'cross' section .of the store of mercury that is in contact withatmospheric air. This arrangement has the result that the setting of themercury store vessel which is requisite for a correct fadju'stment ofthe comparing mercury meniscus, is always independent of the height ofthe place of measurement above sea level and also always independent ofthe fluctuations in the atmospheric air pressure at said place.

An embodiment of this invention is illustrated in the accompanyingdrawings in which:-

Fig. 1 is an elevation of the improved vacuum-meter in the position ofrest.

Fig. 2 illustrates the apparatus in the measuring position, andReferring to Fig. 1, the improved apparatus is composed'of a barometrictube n which is provided at'its upper end with anpends on the lowest sealevel at which it is desired to take measurements.

The adjustment is effected relatively to theaxis y-y and is determinedby the mean barometric column corresponding to the respective sea level;it is also determined by the height p for taking intoconsideration thelocal variations in the barometric height, and the height of the mercurystore vessel 1" (measuring position shown in Fig. 2).

The position of the vessel 7' when the apparatus is at rest (as shown inFig. 1) depends on the highest possible barometric position. Theposition of the stop that is chosen from the above points of view mustbe retained once for all, independently of the sea level and the localvariations in the height of the barometer at the place of use of theapparatus. l.

' When the apparatus, in the rest positio shown in Fig. 1, is placedunder high vacuum by means of its connection .9, the barometric mercurycolumn of, for instance, 730 millimetres is. established. On raising themercury vessel 1" from-the position of rest shown 1n Fig. -1 into themeasuring position shown in Fig. 2, through the distance it (whichisgiven by the stop a) the mercury rises up to the mark to at thelevel yyfrom the tube n into the enlargement 0 which has a large cross section7, and also into the bulb m and to a height in the tube is depending onthe degree of vacuum under measurement, compressing the gaseous contentof the branch 0, m, is into the upper part of is; the mercury flowingout of the vessel 1 so that the bottom surface of mercury goes back tothe annular surface f, comprised between thg inner and outer parts ofthe barometric tu e.

two cross sections f and is chosen such? Y that any variations in theheight of the mer- The proportion between the areas of the.-.

the measuring position are transferred to the lower mercury level f,where they have no influence upon the measurement. The height of thevessel 1- above its rest position is therefore in all cases the same forthe measuring pbsition so that instead of this adjustment being effectedaccording to the upper level of the mercury as in the hitherto employedform ofthe apparatus, it can now, in the improved form, be effected inrelation to the stop a after the latter has been fixed once for all.

The upper mercury level can therefore be invisible and the barometrictube 71. together with the upper expansion vessel 0 and the branch i mayall be made of metal.

What I claim is i 1. A vacuum meter of the McLeod type including agraduated capillary tube, a barometric tube communicating with thecapillary tube and having an enlarged bore at its upper end, a storagevessel surrounding the lower end-of the barometric tube, the crosssection of said enlarged bore being Very great in proportion to thecross-section of the space between the lower part of the barometric tubeand the walls of the mercury storage vessel for the purpose of renderingthe adjustment of the mercury storage vessel which is necessary for theproper .adjustmentof the comparing mercury meniscuspracticallyindependent-of variations of atmospheric pressure.

2. A vacuum meter as claimed in claim 1 in which the mercury storagevessel has an internal cross-sectional area only slightly larger thanthe external cross-section of the barometric tube, the barometric tubebeing slidable telescopically in said storage vessel.

3. A vacuum meter as claimed in claim 1 in which the mercury storagevessel has an internal cross' sectional area only slightly larger thanthe external cross section of the barometric tube, the barometric tubebeing slidable telescopically in said storage vessel, and a stop fixedrelatively to the barometric .tube and engageable with the storagevessel for determining the upper limit of move

